A supernova is really the biggest explosion that humans have ever seen. Each blast is the extremely bright, super-powerful explosion of some star.
Massive stars really burn huge amounts of nuclear fuel at their cores, or centers. This produces tons of powerful energy, so the center gets very hot. Heat generates pressure, and the pressure created by a star’s nuclear burning also keeps that star from collapsing.
A star is in balance between 2 opposite forces. The star’s gravity tries to squeeze the star into the smallest, tightest ball possible. But the nuclear fuel burning in the star’s core creates strong outward pressure. This outward push resists the inward squeeze of gravity.
These fantastic spectacular space events can be so bright that they outshine their entire galaxies for a few days or even months. They can be seen across the universe.
If you are seeing a star explode in the sky, it might have actually exploded more than 13,000 years ago. Light travels at the speed of light.
The speed of light = 299 792 458 m / s
The so-called "speed of light" in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as 299792458 metres per second (approximately 300000 km/s, or 186000 mi/s). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. According to special relativity, c is the upper limit for the speed at which conventional matter, energy or any signal carrying information can travel through space.